1. Field of the Invention
This invention relates to a steering apparatus for an outboard motor comprising an electric actuator unit.
2. Description of the Related Art
Conventionally, there has been known a steering apparatus for an outboard motor in which a hydraulic pump is provided on, for example, a helm (steering wheel), and a hydraulic actuator configured to be driven by the hydraulic pump is disposed near the outboard motor. In this steering apparatus, an oil pressure produced by the hydraulic pump serves to redirect the outboard motor. Also known is a mechanical steering apparatus that redirects an outboard motor by transmitting a rotary motion of a helm to the outboard motor through a push-pull cable. Since these steering apparatuses are operated manually (or by an operator's power), they require a considerably large operating force, depending on the boat operating conditions, and hence, leave room for improvement.
Thus, as disclosed in, for example, Japanese Patent No. 2959044 (Patent Document 1), a steering apparatus may be contrived such that an electric actuator unit is used as a drive source for steering. The steering apparatus of Patent Document 1 comprises a rack extending transversely relative to a boat body, pinion meshing with the rack, rack case that accommodates the pinion, electric motor for rotating the pinion, and gear mechanism for transmitting a rotational force of the electric motor to the pinion. When the pinion is rotated by the electric motor, the pinion and rack case move longitudinally relative to the rack. The outboard motor can be redirected as the movement of the rack case is transmitted to the outboard motor through a transmission mechanism comprising a guide plate. According to the electric steering apparatus of this type using the electric motor for steering, its helm requires only a small operating force, so that a burden on an operator can be reduced.
In the electric steering apparatus using the rack and pinion, as described in Patent Document 1, the pinion, gear mechanism, and drive system components, such as the electric motor, project outside the rack, so that the longitudinal dimension and the like are large. The steering apparatus of this type has a problem that various cables, fuel supply pipe, etc., attached to the outboard motor are likely to interfere with the drive system components.
In addition, protective boots (bellow tubes) for waterproofing a fitting portion between the rack and pinion are exposed to the outside. Therefore, the cables, fuel supply pipe, etc., may possibly contact the protective boots. In some cases, the protective boots may be damaged and leave the rack and pinion to be eroded by seawater or the like. As the drive system components pivot downwardly when the outboard motor is tilted up, moreover, the greatly projecting drive system components are likely to interfere with members on the boat body, thus leaving room for improvement.